Designing and manufacturing semiconductor integrated circuits is a challenge. Variations in semiconductor processing of an integrated circuit can cause changes in its performance and yield. In nanometer technologies, the performance of a given semiconductor chip can vary as much 30% due to process variations. The performance of a chip is also affected by environmental variations, such as variations in temperature or supply voltage. It is desirable to consider semiconductor processing variations in the design of the integrated circuit, including when performing a static timing analysis of the integrated circuit.